The present invention relates to a high-precision pressure sensor. More particularly, the invention relates to a pressure sensor which is adapted to detect pressure in extruders of plastic materials, plastic films, synthetic fibers and the like.
It is known that pressure sensors used for example in the case of extruders of plastic materials, plastic films, synthetic fibers and the like comprise a rod-like element at a first end of which there is provided a membrane on the face of which a strain-gauge is arranged. The rod-like element is filled with a fluid, such as mercury or oil, and the compression of the fluid by the mass of plastic material whose pressure is to be measured applies an action to the strain gauge, which accordingly produces an electrical signal which is then interpreted by an electronic system connected to the pressure sensor.
The drawback of this pressure sensor is that it wears rapidly, since the melted plastic material easily damages the membrane, owing to its limited thickness. Accordingly, it is necessary to replace the pressure sensor; most of all, this entails the need to dispose of the mercury or oil, with considerable costs, since for example mercury is highly polluting and precise standards must be followed for its disposal.
Pressure sensors are further known which are constituted by a rod-like element, one end of which is provided with an element for the mechanical transmission of pressure which acts on a chip of semiconductor material on one face of which the strain-gauge is arranged. In practice, the semiconductor chip behaves like the membrane of the above-described sensor.
The presence of a semiconductor chip allows to solve the problem of the fluid, mercury or oil, which accordingly is no longer necessary.
The semiconductor chip is usually accommodated in an appropriately provided cavity formed in a block, made for example of alumina, from which metallized terminals extend which are suitable to carry the signal that originates from the strain-gauge to the electronic system for processing the signal.
These sensors have a semiconductor chip which is rigidly coupled to the alumina block for example by gluing.
The mechanical transmission element is normally accommodated in a cover which is meant to be coupled to an external metallic enclosure which internally accommodates the alumina block with the corresponding semiconductor chip rigidly coupled thereto.
The advantage of this solution is that the membrane, which in this case is constituted by the chip of semiconductor material, is practically not subject to wear due to friction with the plastic material whose pressure is to be measured.
However, the fact that the semiconductor chip is rigidly coupled to the alumina block that supports it entails that the signals generated as a consequence of pressure sensing may be inaccurate, because of the deformation that may affect the alumina block that accommodates and supports the semiconductor chip.
Therefore, even the above solution is not free from drawbacks, and in particular measurement precision, which is a fundamental requirement, is not ensured absolutely.
The aim of the present invention is to provide a pressure sensor, particularly for an extruder of plastic materials and the like, which has a high measurement precision which is constant over time.
Within the scope of this aim, an object of the present invention is to provide a pressure sensor which is highly resistant.
Another object of the present invention is to provide a pressure sensor, particularly for extruders of plastic materials and the like, in which the alteration of the measurement signal caused by thermal expansions, deformations and the like is reduced to the lowest possible level.
Another object of the present invention is to provide a pressure sensor, particularly for extruders of plastic materials, which is highly reliable, relatively easy to manufacture and at competitive costs.
This aim, these and other objects which will become apparent hereinafter are achieved by a pressure sensor, particularly for use in extruders of plastic materials and the like, which comprises an outer enclosure which is adapted to contain a supporting element for a semiconductor chip which is provided with a strain-gauge on one of opposite faces of said chip, a covering element being provided in order to close said enclosure, a mechanical transmission element being accommodated in said covering element, being directed toward said semiconductor chip and being in contact with said chip, characterized in that said semiconductor chip is accommodated so as to float in said supporting element.